The construction and mining industries make extensive use of explosives in areas increasingly close to existing structures. The power generated by the explosives can have a detrimental effect on business and residential structures and even at lesser levels can cause human discomfort. However, many projects require the use of large explosive charges in order to be economically feasible. Therefore, the extent of vibrations generated due to the explosions must be carefully measured and monitored to insure that the limit of structural damage is not reached but that needlessly small charges are not being used.
A number of seismic monitoring devices have been developed to measure the energy of vibrations generated by explosive charges. An example of such a device is the three-dimensional seismograph disclosed in U.S. Pat. No. 3,872,478 to Lucole. Further seismic recorders are shown in U.S. Pat. Nos. 3,603,140; 2,578,803 and 1,438,462.
The above devices do not fully satisfy the requirements of the mining and construction industries and there exists a need for a seismic recorder which can be operated in a remote location for extended periods of time while recording only seismic events which exceed a predetermined threshold.
In addition, the need exists for a recorder wherein the seismic and acoustic information is recorded in an analog format for detailed engineering analysis which is followed by a recording in a digital format of the summary data attendant to the event, including the year, the day of the year, the hour and minute of the day, the peak particle velocity of the seismic motion, the peak air overpressure, the recording range of seismic data, the internal battery voltage, the instrument identification number, and the event number of the recording. The summary data should be recorded in a digital format to permit automatic processing of the records by computer for fast, accurate and low cost recovery of the key recorded data by inexperienced personnel.